This invention relates to magnetic imaging and more particularly to an improved method of creating latent magnetic images on magnetizable recording media via magnetic interpositives.
There has recently been introduced a magnetic imaging system which employs a latent magnetic image on a magnetizable recording medium which can then be utilized for purposes such as electronic transmission or in a duplicating process by repetitive toning or transfer of the developed image. Such latent magentic image is provided by any suitable magnetization procedure whereby a magentized layer of marking material is magnetized and such magnetism transferred imagewise to the magnetic substrate. Such a process is more fully described in U.S. Pat. No. 3,804,511 to Rait et al.
As is disclosed in that patent, an optical image can be reproduced by first reducing it to a graphical image but employing a magnetizable marking material. Such magentizable material is typically electroscopic toner comprising a ferromagentic magerial which, after image formation is susceptible to magnetization. There is thus formed an imagewise pattern of magnetization which pattern is then transferred to a magnetic substrate by any one of several methods as disclosed in the patent. Preferably, the magnetization in imagewise pattern is produced in a magnetic substrate by the anhysteretic method whereby the magnetized graphic image is brought into intimate contact with a magnetic substrate and while in contact is subjected to an A.C. signal from a recording head. The magnetic substrate is thereby magnetized in image configuration in accordance with the graphic image. Other methods of utilizing the magnetized graphic image for producing a latent magnetic image are also disclosed such as by providing intimate contact between the graphic magnetic material and a previously uniformly magnetized substrate and applying an erase signal through the graphic image support thereby applying the magnetic image as a shunt for the erase signal. There is thus produced by selective erasure in background areas a latent magnetic image in those areas shunted by the magnetic graphic image. Various other methods of providing such latent image utilizing a previously formed magnetizable graphic image are disclosed in the patent referred to above.
One desires to form a latent magnetic image having the highest possible degree of magnetization such that its detection by any of the several methods is facilitated. The process variations inevitable in prior art imaging systems whereby the magnetizable graphic image is produced causes variations in toner depth, uneveness of the surface of the image and background problems. Such variations make difficult the creation of high quality latent magnetic images by the methods referred to in the prior art.
Furthermore, the electrostatographic, including xerographic techniques utilized to provide the magnetized graphic image interpositive for producing a latent magnetic image on a magnetizable recording medium requires the use of a toner which is properly triboelectrically charged so as to become attracted to the latent electrostatographic image. The toner must also contain magnetizable materials so that the developed electrostatographic image can be magnetized to form the magentic interpositive. The inclusion of magnetic materials in the toner invariably adversely affects the triboelectric characteristics of the toner and thereby resulting in a loss of quality in the developed image from that which would ordinarily be obtained upon developing the same latent electrostatographic image with commercially available toner which does not contain a magnetic component.
Further, recording heads used in transferring the magnetic signal from the magnetized interpositive to a magnetizable recording medium typically have a lifetime of only a few hundred of hours. This presents a significant reliability problem in magnetic imaging schemes.
The present invention provides an improved interpositive magnetic imaging scheme wherein a preferred pathway of interpositive magnetic imaging is provided.